Continuous dynode channel type secondary electron multiplier

ABSTRACT

A continuous dynode channel type secondary electron multiplier wherein an electric field is established in the axial direction, and a secondary-electron emissive surface is provided on the inner surfaces of the channel dynode, said secondary electron multiplier being so constructed that an electric field component perpendicular to the axis is varied along the axial direction to increase the total number of impacts of electrons with the secondary-electron emissive surfaces per unit axial length, thereby enhancing the multiplication factor.

United States Patent 1 [111 3,735,184

Maeda 5] May 22, 1973 CONTINUOUS DYNODE CHANNEL [56] References Cited TYPE SECONDARY ELECTRON MULTIPLIER UNITED STATES PATENTS 2,141,322 12/1938 Thompson ..328/242 [75] Invent Maeda 2,232,900 2/1941 Brewer .313 105 Japan 2,369,230 2/1945 Hansell.... ...32s/243 x Assignee: 3,349,273 10/1967 Gregg Ltd. Os k J a a apan Primary ExaminerRobert Sega] Filed? 19, 1971 Attorney-Stevens, Davis, Miller & Mosher 21 A l. N 173,229 1 pp 57 ABSTRACT Related Apphcamm Data A continuous dynode channel type secondary electron [63] Continuation of Ser, No, 790,744, Ja 13 9 9 multiplier wherein anelectric field is established in the v abandoned axial direction, and a secondary-electron emissive surface is provided on the inner surfaces of the channel [52] US. Cl. ..3l3/l05, 313/95, 328/243 dynode, Said secondary electron multiplier being so [51] Int. Cl .1101] 43/20 constructed that an electric field component perpen- [58] Field of Search ..H01j/43/24; 313/95, dic lar to h xi i v ri long the axial direction to increase the total number of impacts of electrons with the secondary-electron emissive surfaces per unit axial length, thereby enhancing the multiplication factor.

5 Claims, 11 Drawing Figures Patented May 22, 1973 3 Sheets-Sheet 1 F/G.3a

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ATTORNEYS Patented May 22, 1973 3 Sheets-Sheet 5 INVI'QZNTOR Hmmo H0509 ATTORNEU CONTINUOUS DYNODE CHANNEL TYPE SECONDARY ELECTRON MULTIPLIER CROSS-REFERENCE TO RELATED APPLICATION This is a continuation of Ser. NO. 790,744, filed Jan. I3, 1969, and now abandoned. Y

This invention relates to improvements in the construction of secondary-electron emissive dynodes pro vided on parallel plates defining a continuous channel type electron multiplier. 7

It is an object of the present invention to provide a photomultiplier tube which is small-sized and capable of achieving a high multiplication factor as compared with the conventional continuous channel type parallel plate secondary electron emissive dynode.

Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which: I

FIG. 1 is a perspective view illustrating the construction and operation of a parallel plate channel type sec ondary electron multiplier used for the conventional photomultiplier; I

FIG. 2 is a longitudinal sectional view showing the channel type secondary electron multiplier according to an embodiment of the present invention;

FIGS. 3a and 3b are an inner view and a longitudinal sectional view showing the planar inner resistance film adapted for secondary-electron emissive dynode which constitutes the present invention, respectively;

FIGS. 40 and 4b are an inner view and a longitudinal sectional view showing another example of the parallel plate secondary electron emissive dynode constituting the present invention, respectively;

FIG. 4c is an equivalent circuit diagram showing the resistance distribution of the plate shown in FIGS. 4a

and 4b;

FIGS. 5a and 5b are an inner view and a longitudinal sectional view showing the connection between the resistance film and the secondary-electron emissive dynode surface constituting the channel type parallel plates secondary electron multiplier according to the present invention; 7

FIG. 6 is a schematic view showing thechannel type secondary electron multiplier tube according to a second embodiment of the present invention; and

FIG. 7 is a perspective view showing the channel type secondary electron multiplier tube according to a third embodiment of the present invention.

The preferred embodiments of the present invention will now be described with reference to the drawings.

Description will first be made of the conventional channel type secondary electron multiplier, with reference to FIG. 1, wherein the reference numeral 1 represents base plates which construct a parallel plate-like channel formed by an insulator material such as glass, ceramic or the like, and 2 a resistance film layer formed by a metal or semiconductor having as high a secondary-electron emission ratio as possible and representing a high resistance value in the axial direction, the resistance layer being formed on the inner surface of the channel base plate 1 by an evaporation or other suitable method. The resistance layer 2 constitutes a continuous secondary electron emissive dynode the surface of which serves as resistive network. It also serves to distribute an acceleration voltage applied thereto from the outside in the axial direction of the channel constituted by the continuous dynode, thereby establishing an axial electric field within the channel, whereby secondary electrons are accelerated in the axial direction. The reference numeral 3 indicates a primary-electron beam which is entered at such a speed that secondary-electron emission is most likely to be caused in the neighborhood of the entrance of the channel 1, and then bombarded onto the secondaryelectron emissive surface 2 constituting the inner surface of the channel 1, thus resulting in secondary electrons being emitted. The secondary electrons thus initially emitted are accelerated along a parabolic path by the axial electric field established within said channel so as to be bombarded onto the opposite secondaryelectron emissive surface of the channel dynode, so that further secondary electrons 4 are emitted therefrom.

As a result of the repetition of such operation, the secondary electrons are increased by geometrical progression, while being advanced from the left to the right as viewed in FIG. 1. The reference 5 denotes the resulting output electron current which is collected at a collector 6. The reference numeral 7 indicates an acceleration voltage source which is applied across the both ends of the resistance film layer 2 constituting the continuous dynode thereby to accelerate secondary electrons 4 occurring within the channel to the right. The reference numeral 8 represents a DC power source for giving a positive potential to the collector for the purpose of guiding the secondary-electron stream taken from the Output end to the collector.

As described above, with the conventional channel type secondary electron multiplier, in order to accelerate electrons within the channel from the left to the right as shown in the drawing, it is necessary to establish a uniform acceleration field. In the case of the channel defined by the parallel flat plates, therefore, a uniform thin film of metal or semiconductor is provided on each of the inner surfaces of the opposing plates, and an acceleration voltage is applied across the input and output ends of the channel plate, so that the potential within the channel is made progressively higher from the entrance side toward the exit side with the aid of the high-resistive layers 2 provided on the inner surfaces of the channel plate. The resistance of the high-resistive layer 2 may assume a value in a range determined from the quantity of the multiplied secondary electrons, and it is nonnally selected to be several tens M0 to several hundreds M0 or higher.

In the parallelplate channel type secondary electron multiplier, the direction of the acceleration for the secondary electrons is parallel to the axis (the direction in which electrons are multiplied), and the continuous secondary-electron emissive surface of the dynode plates are also parallel to the axis. Therefore, unless secondary electrons emitted from the emissive surface are made to travel a considerably long distance prior to their bombardment onto the opposite secondaryelectron emissive surface, the next impact will never take place. The smaller the spacing between the parallel plates as compared with the axial length of the channel, the larger number of the impacts of the secondary electrons onto the opposite secondary-electron emissive surfaces of the dynode plate as shown in FIG. 1. In other words, it is desired that the ratio of the spacing to the axial length of the channel be made low in order to increase the multiplication factor. For this reason,

the channel length should be increased to obtain a multiplier with a high multiplication factor. In accordance with the present invention, however, an attempt is made to positively add an electric field perpendicular to the axis to an axial electric field, without effecting the acceleration of multiplied secondary electrons solely by such axial electric field.

Description will next be made of examples of improvements in the continuous dynodes for various channel type secondary electron multipliers. The dynodes employed in the various embodiments of this invention, and especially those of FIGS. 2, 3, 4 and 5, may be constructed of a thin film of metal, such as nickel, molybdenum or tungsten, formed on an insulating base, such as quartz, glass, ceremic, etc.; the metal film may be sensitized with cesium or other metal, such as lithium. Examples of these and other applicable materials are found in U.S. Pat. No. 2,141,322 to Thompson. Referring first to FIG. 2, there is shown an embodiment of the present invention wherein the secondaryelectron emissive layers formed on the inner surfaces of the parallel plates constituting the channel are divided into a plurality of sections. The divided sections of the opposing plates are disposed in staggered relationship with each other, and they are supplied with potentials from an external power source through series divider resistors by which potentials are made successively higher from the left to the right as shown in the drawing. Parts of FIG. 2 corresponding to those of FIG. 1 are indicated by similar reference numerals, and further description thereof will be omitted. With the arrangement shown in FIG. 2, multiplied secondary electrons 4 within the channel are made to collide much more frequently with the secondary-electron emissive surfaces 2 of the dynode, so that as compared with other arrangements having the same channel length and spacing, a much higher multiplication factor can be obtained, although it is necessary to increase the acceleration power source voltage 7 by an amount corresponding to the increase in the number of impacts. n the other hand, if it is desired to achieve the same average number of impact as that in the FIG. I arrangement, and the power source voltage 7 remains the same, then the axial length of the channel may be much shorter to realize the same multiplication factor.

Various methods are conceivable to form the secondary-electron emissive surfaces of the continuous dynode on the inner surfaces of the channel defined by the parallel plates in order to construct such parallel plate type secondary electron multiplier as shown in FIG. 2. FIG. 3 illustrates an example of such methods, the inner surface of one of the plates constituting the channel being shown at a, and the cross section of said one plate being shown at b. The reference numeral 1 represents a base plate formed by an insulator material such as glass, ceramic or the like on which are provided films 21 of a secondary electron emissive material by means of evaporation, sputtering, plating or the like, each of the films 21 being divided in a plurality of sections which are connected in series with each other through high-resistive films 22 for voltage division to thereby constitute a continuous dynode. In FIG. 3a, these resistance films are disposed in staggered relationship with each other so as to present a zig-zag shape as a whole. However, the resistance films connecting the films 21 in series with each other to constitute the continuous dynode may be provided on one side of the secondary electron emissive surface, on opposite sides thereof or in all the gaps between the respective sections, ifthey are made uniform as desired.

FIG. 4 shows a second example wherein the secondary-electron emissive surface and voltage dividing resistors are not separated from each other, and a highresistive film 23 consisting of a semiconductor thin film, metal thin film or the like are provided in a zig-zag manner on aninsulating base channel plate ,1 of glass, ceramic or the like. FIG. 4a shows the pattern of the high-resistive film defining the continuous dynode secondary-electron emissive surface which serves also as voltage dividing resistor, FIG. 4b is a longitudinal sectional view thereof, and'FIG. 4c is an equivalent circuit showing the resistance distribution in the high-resistive film. FIG. 5 shows an arrangement comprising a secondary-electron emissive surface divided in a plurality of sections, voltage dividing resistance films 25 extending along the rear surface of an insulating base plate 1 of glass, ceramic or the like to connect the secondaryelectron emissive surface sections in a flat spiral fashion, and conductive connector members 26 provided on the cutting sides of the glass plate to successively connect said resistance films 25 with the secondaryelectron emissive surface 24. In either case, the base plates each comprising divided secondary-electron emissive surface sections such as shown in FIG. 3, 4 or 5 and voltage dividing high-resistive members connecting said sections in series with each other to constitute a continuous secondary electron emissive dynode are disposed in opposing relationship to each other, the surface sections are arranged in staggered relationship with each other, and potentials applied to these surface sections are made successively higher, so that secondary electrons produced in the continuous stages are multiplied as described above in connection with FIG. 2. With this improved arrangement of continuous dynode surface of secondary-electron multiplier, an electric field component perpendicular to the axial direction is also produced since those portions of the continuous dynode which are opposed to each other are not at the same potential, so that the number of impacts of the secondary electrons with the secondary-electron emissive surface of the channel plate can be increased. Thus, it is possible to obtain a parallel plate channel type secondary electron multiplier which is of high gain, sm all-size and high efficiency.

Furthermore, in accordance with the present invention, besides the foregoing various embodiments using parallel plates, there is also provided a miniaturized channel type secondary electron multiplier with a high gain wherein the continuous multiplier dynodes thereof are not constructed in the form of parallel plates but in a special form such as a curved-face form to intentionally curve the acceleration filed within the electron multiplying channel for the purpose of producing an electric field component perpendicular to the axial direction to increase the number of impacts of the secondary electrons with the secondary-electron emissive surfaces. Description will now be made of examples of such hecondary electron multiplier. Referring to FIG. 6, the reference numeral 1 represents an insulating base plate of glass, ceramic or the like configured in the form of twisted parallel plates. The reference numeral 2 represents a secondary-electron emissive material of high-resistivity formed on the inner surface of the base channel plate 1. Such film 2 may be eliminated by forming the base plate 1 by use of glass of a relatively high resistance which contains a substance of a high resistivity and high secondary-electron emission ratio.

Furthermore, by forming the continuous dynode by a special ribbon l as shown in FIG. 7, the acceleration electric field within the tube is intentionally curved to produce not only an axial acceleration field component but also an acceleration field component perpendicular to the axis, thereby increasing the number of impacts of secondary electrons within the secondary electron emissive surface of the channel plates. By such improvements in the channel construction, it is possible to obtain a photomultiplier with a channel type secondary electron multiplier capable of producing a gain substantially equal to that of the parallel plate type one with a reduced channel length and yet achieving a high multiplication factor. Thus, by changing the configuration of the continuous dynode, there is produced not only an axial electric field component but also an electric field component perpendicular to the axial direction, thereby increasing the number of impact of secondary electrons with the secondary-electron emissive surfaces of the dynode and the total multiplier sensitivity.

What is claimed is:

1. A channel-type secondary electron multiplier, comprising:

a pair of parallel spaced flat plates of an electrically insulating material defining an electron multiplying channel therebetween;

a plurality of secondary electron emissive film sections made of a secondary electron emissive material having a finite surface electrical resistivity, said film sections being disposed on said plates and spaced apart from each other on the respective plates a distance substantially less than the width of a given film section, the position of the film sections along one plate being staggered with respect to those along the other plate;

a plurality of resistance elements disposed on said plates in the spaces defined between adjacent emissive film sections and electrically coupled thereto to form a series electrical circuit of alternating resistance elements and secondary emissive film sections;

a DC. voltage source coupled across the series combination of resistance elements and emissive film sections on each plate; and

means for collecting the multiplied secondary electrons.

2. A multiplier according to claim 1, wherein said resistance elements are formed of a material having a substantially different resistivity than said secondary electron emissive film material, said resistance elements being directly connected electrically to immediately adjacent ones of said emissive film sections.

3. A channel-type secondary electron multiplier, comprising:

a pair of parallel spaced flat plates of an electrically insulating material defining an electron multiplying channel therebetween;

a continuous coating formed of a secondary electron emissive material having a finite surface electrical resistivity and deposited on the opposed surfaces of said flat plates, said coating being formed of alternating first and second portions, said first portions having a substantially larger surface area than said second portions, the first portions disposed on one plate being longitudinally staggered in relation to the corresponding first portions disposed on the other plate,

said second portions being formed in a portion of the spaces defined between adjacent first portions on each plate, said second portions being provided primarily as voltage dividers for positively and discontinuously increasing voltage potentials across successive first portions in the direction of flow of a DC. voltage source connected across the longitudinally opposite ends of the coatings on each of said plates; and

means at the output of said multiplier for collecting multiplied secondary electrons.

4. The multiplier according to claim 3, wherein said first and second portions are disposed in a zig-zag pattern on each plate.

5. A channel-type secondary electron multiplier, comprising:

a pair of parallel spaced flat plates of an electrically insulating material defining an electron multiplying channel therebetween;

a plurality of secondary electron emissive film sections made of a secondary electron emissive material having a finite surface electrical resistivity, said film sections being disposed on and spaced apart from each other on each plate a distance substantially less than the width of a given secondary electron emissive film section, the positions of the film sections on one plate being staggered in the longitudinal direction from those on the other plate;

a plurality of resistance elements made of a material having a substantially different resistivity than the secondary electron emissive material, said resistance elements being disposed in band-shaped pat terns on the opposite surfaces of said plates from said emissive film sections, each band-shaped resistance element extending from one lateral side of the plate adjacent a first film section, to the laterally opposite side of said plate adjacent the next adjacent film section;

means electrically coupling the respective ends of each resistance element to the corresponding adjacent emissive film section, said resistance elements and emissive film sections forming a series electrical circuit of alternating resistance elements and emissive film sections;

a DC. voltage source coupled across the series combination of said resistance elements and emissive film sections on each plate; and

means for collecting the multiplied secondary electrons. 

1. A channel-type secondary electron multiplier, comprising: a pair of parallel spaced flat plates of an electrically insulating material defining an electron multiplying channel therebetween; a plurality of secondary electron emissive film sections made of a secondary electron emissive material having a finite surface electrical resistivity, said film sections being disposed on said plates and spaced apart from each other on the respective plates a distance substantially less than the width of a given film section, the position of the film sections along one plate being staggered with respect to those along the other plate; a plurality of resistance elements disposed on said plates in the spaces defined between adjacent emissive film sections and electrically coupled thereto to form a series electrical circuit of alternating resistance elements and secondary emissive film sections; a D.C. voltage source coupled across the series combination of resistance elements and emissive film sections on each plate; and means for collecting the multiplied secondary electrons.
 2. A multiplier according to claim 1, wherein said resistance elements are formed of a material having a substantially different resistivity than said secondary electron emissive film material, said resistance elements being directly connected electrically to immediately adjacent ones of said emissive film sections.
 3. A channel-type secondary electron multiplier, comprising: a pair of parallel spaced flat plates of an electrically insulating material defining an electron multiplying channel therebetween; a continuous coating formed of a secondary electron emissive material having a finite surface electrical resistivity and deposited on the opposed surfaces of said flat plates, said coating being formed of alternating first and second portions, said first portions having a substantially larger surface area than said second portions, the first portions disposed on one plate being longitudinally staggered in relation to the corresponding first portions disposed on the other plate, said second portions being formed in a portion of the spaces defined between adjacent first portions on each plate, said second portions being provided primarily as voltage dividers for positively and discontinuously increasing voltage potentials across successive first portions in the direction of flow of a D.C. voltage source connected across the longitudinally opposite ends of the coatings on each of said plates; and means at the output of said multiplier for collecting multiplied secondary electrons.
 4. The multiplier according to claim 3, wherein said first and second portions are disposed in a zig-zag pattern on each plate.
 5. A channel-type secondary electron multiplier, comprising: a pair of parallel spaced flat plates of an electrically insulating material defining an electron multiplying channel therebetween; a plurality of secondary electron emissive film sections made of a secondary electron emissive material having a finite surface electrical resistivity, said film sections being disposed on and spaced apart from each other on each plate a distance substantially less than the width of a given secondary electron emissive film section, the positions of the film sections on one plate being staggered in the longitudinal direction from those on the other plate; a plurality of resistance elements made of a material having a substantially different resistivity than the secondaRy electron emissive material, said resistance elements being disposed in band-shaped patterns on the opposite surfaces of said plates from said emissive film sections, each band-shaped resistance element extending from one lateral side of the plate adjacent a first film section, to the laterally opposite side of said plate adjacent the next adjacent film section; means electrically coupling the respective ends of each resistance element to the corresponding adjacent emissive film section, said resistance elements and emissive film sections forming a series electrical circuit of alternating resistance elements and emissive film sections; a D.C. voltage source coupled across the series combination of said resistance elements and emissive film sections on each plate; and means for collecting the multiplied secondary electrons. 